Field of the Invention
The present invention relates to a wiring board soldered with lead wire and an electronic device comprising the wiring board.
Description of the Related Art
In recent years, electronic devices have been downsized and becoming thinner. In a device where incorporated components are highly densified, a space for extending lead wire is limited with less flexibility. In such circumstances, it is desirable to suppress variation in a leading direction of the lead wire or variation in tip position in the leading direction when the lead wire is soldered to a soldering land included in a printed wiring board for connection thereto. Therefore, it is desirable to perform soldering by positioning the lead wire in and at an appropriate direction and a position in the land.
Therefore, technique to mount lead wire at an appropriate position on a land is disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2014-135392. In Japanese Laid-Open Patent Publication (Kokai) No. 2014-135392, a leading direction of lead wire is positioned by providing a solder ball in advance, on a land of a printed wiring board, adjacent to an area for mounting the lead wire.
In the related art disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2014-135392, however, a dedicated special device is required for forming the solder ball on the soldering land. Therefore, there is a problem that implementation is difficult in a general step of manufacturing a printed wiring board mounted with components.
Furthermore, for determination of a direction of the lead wire, generally, the shape of a land is formed to be a rectangular or an ellipse such that a direction where the lead wire is desired to be led corresponds to a longitudinal direction thereof. The lead wire is soldered according to the shape. In operation of soldering, however, a position or direction of the lead wire varies in the land. In this case, it is difficult to appropriately extend the lead wire in a limited space in a device.
Moreover, generally employed is a method to provide cream solder to a soldering land in advance in a printing step of cream solder before reflow mounting of mounting components onto the printed wiring board and to allow formation of preliminary solder after completion of the reflow mounting. Forming the preliminary solder can enhance working property of soldering. However, since soldering is performed by heating up and melting solder while lead wire is placed on the preliminary solder, the degree of floating of the lead wire from a substrate after soldering is not constant due to variation in the work and thus the height varies. In order to downsize devices and implement thinner devices, it is desirable to keep the height of the lead wire from the substrate as low as possible and constant after soldering.